Audio signal processing, sometimes referred to as audio processing, is the processing of a representation of auditory signals, or sound. The audio signals, or sound may be in digital or in analog data format. The analog data format is normally electrical, wherein a voltage level represents the air pressure waveform of the sound. A digital data format expresses the air pressure waveform as a sequence of symbols, usually binary numbers. The audio signals presented in analog or in digital format may be processed for various purposes, for example, to correct timing of the audio signals.
Currently, audio signals may be generated and modified using a computer. For example, sound recordings or synthesized sounds may be combined and altered as desired to create standalone audio performances, soundtracks for movies, voiceovers, special effects, etc. To synchronize stored sounds, including music audio, with other sounds or with visual media, it is often necessary to alter the tempo (i.e.; playback speed) of one or more sounds.
Generally, a loop in audio processing may refer to a finite element of sound which is repeated using, for example, technical means. Loops may be repeated through the use of tape loops, delay effects, cutting between two record players, or with the aid of computer software. Many musicians may use digital hardware and software devices to create and modify loops, often in conjunction with various electronic musical effects. Live looping is generally referred to recording and playback of looped audio samples in real-time, using either hardware (magnetic tape or dedicated hardware devices) or software. A user typically determines the duration of the recorded musical piece to set the length of a loop. The speed or tempo of playing of the musical piece may define the speed of the loop. The recorded piece of music is typically played in the loop at a constant reference tempo. New musical pieces can be recorded subsequently on top of the previously recorded musical pieces played at a tempo of the reference loop.
Because the tempo and/or speed of recording of the new musical pieces may change, the loops of the newly recorded musical pieces may be non-synchronized to each other. The lack of synchronization between the musical pieces can severely impact a listening experience. Therefore, after being recorded, the tempo of the new musical pieces may be changed to the constant reference tempo of the previously recorded musical piece played in the reference loop.
Unfortunately, merely changing the tempo of all newly recorded musical pieces to a constant reference tempo may result in undesired audible side effects such as pitch variation (e.g., the “chipmunk” effect of playing a sound faster) and clicks and pops caused by skips in data as the tempo of the newly recorded pieces is changed. Currently there are no ways to dynamically adjust the tempo of the musical pieces during recording.